Bar magnets have two poles. They make dipole magnetic fields. Magnetic fields can have more than two poles. Quadrupole fields have four poles.
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Original artwork by Windows to the Universe staff (Randy Russell).
Dipole, Quadrupole, and Multipole Magnetic Fields
Have you ever seen a bar magnet? Bar magnets have two magnetic poles - north and south. The magnetic field around a bar magnet is called a dipole magnetic field. "Dipole" means "two poles".
Bar magnets are not the only things that make dipole fields. Electricity flowing through a coiled wire can cause a dipole magnetic field. The magnetic fields of some planets are pretty much dipole fields.
Dipoles are not the only shape magnetic fields come in. There are also quadrupole fields with four poles. Sometimes magnetic fields have six or even eight poles (an octupole!). Any field with more than two poles is called a multipole field.
Some planets, stars, and moons have magnetic fields. Some of those magnetic fields are pretty much dipoles. Others are more complex. They have a mix of dipole and multipole magnetic fields. The magnetic fields of Earth and Jupiter are mostly dipoles. They only have weak multipole parts. Uranus and Neptune have more complicated magnetic fields. The quadrupole parts of their fields are just as strong as the dipole parts!
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The force of magnetism causes material to point along the direction the magnetic force points. As shown in the diagram to the left, the force of magnetism is illustrated by lines, which represent the force.
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The Earth is a good example of a planetary dipole, where the lines of force point in a direction out of the South (magnetic) Pole and into the North (magnetic) Pole. Planets can also show evidence of quadrupoles
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Jupiter's magnetosphere is very special. It is the biggest thing in the entire solar system. Not only is it big enough to hold all of Jupiter's moons, but the sun itself could fit inside. It goes all
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The magnetosphere of Uranus is medium sized, but still much bigger than the Earth's. It holds all of Uranus' moons. It is probably made in the middle of the planet, and with ice, rather than with iron
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Uranus has a strange magnetic field. The magnetic poles of Uranus are not at all close to the geographic poles of Uranus. The main magnetic field of Uranus is tilted 59° away from the planet's spin axis.
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The Sun has a very large and very complex magnetic field. The magnetic field at an average place on the Sun is around 1 Gauss, about twice as strong as the average field on the surface of Earth (around
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Mercury has a magnetic field. Its field is weak. Earth's magnetic field is tilted, and so is Mercury's. That means Mercury's magnetic poles are not in the same place as its geographic poles. Mercury has
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